A new online calculator meant to measure cholesterol risk — rolled out just last week by the nation’s leading heart organizations along with new cholesterol-lowering guidelines — is so riddled with problems that leading cardiologists are calling for a halt in implementation to the new cholesterol-fighting strategy.

Last Tuesday, the American Heart Association and the American College of Cardiology unveiled a new strategy for battling heart disease, which called for doubling the number of Americans on statins, or cholesterol-lowering drugs. They also introduced an online calculator designed to help doctors assess risk of heart disease. But the calculator turns out to be flawed, overestimating cardiovascular risk, experts tell the New York Times. As the calculator is designed now, it could recommend statin drugs to millions of Americans who do not need them.

Two Harvard Medical School professors identified the problem in findings that will be published on Tuesday in the Lancet, a major medical journal. The professors, Dr. Paul M. Ridker and Dr. Nancy Cook, pointed out the problems in the calculator earlier this year when the National Institutes of Health’s National Heart, Lung and Blood Institute — which originally developed the guidelines — sent drafts to several professors for review. Though Ridker and Cook reported their concerns at the time, nothing was changed about the calculator before it was released last week. Now, in light of the problems, leading cardiologist Dr. Steven Nissen — chief of cardiovascular medicine at the Cleveland Clinic and a past president of the American College of Cardiology — called for a halt on Sunday to implementation of the new guidelines.

“It’s stunning,” Nissen told the Times. “We need a pause to further evaluate this approach before it is implemented on a widespread basis.”

The American Heart Association also called an emergency session at their annual meeting in Dallas on Saturday night to address the problem, the Times reports. The group reportedly held private meetings with Ridker, whose calculations with Cook indicate that the calculator could be overpredicting cardiovascular risk by 75% to 150%, depending on the population. Later, both the American Heart Association and the American College of Cardiology said while the calculator is not perfect, it is still a big step forward. They recommended that doctors still follow the guidelines released last week and discuss treatment options with their patients, but advised against blind adherence to the calculator.

“We need to see if the concerns raised are substantive,” Dr. Sidney Smith, the executive chairman of the guidelines committee, told the Times. “Do there need to be changes?”